The present invention relates to a method of increasing process capacity when microfiltrating a fermentation-derived product.
Microfiltration has been the target for much research and development over the last years. Especially developments in hardware and membranes have been at focus. However two issues still limit the use of microfiltration within recovery of fermented biomolecules. Low fluxes and often also low transmission are the limiting factors for success. Often a process can be developed based on microfiltration for harvest of such products, however in many cases the process will not be able to compete with the more traditional solid liquid separation techniques like centrifugations and drum-filtrations. This is especially the case in continuous large scale processes where fouling necessitates frequent CIP (cleaning-in-place) for maintaining high transmission and flux.
Especially within the biotechnology industry fouling has been an almost unsolvable problem regarding microfiltration of fermentation broths. This is due to the fact that fermentation broths contain besides the product of interest numerous impurities like other intracellular and extracellular metabolites, lysed cells, substrate components, nucleic acids, defoaming agents etc.
Much focus has therefore been allocated to development of hydrophilic membranes and of improved microfiltration hardware with technologies such as back wash/back shock and mechanical induced shear as the more successful developments.
On the operational side focus has been on precise control of trans-membrane pressure and of control of maximum permeate flow rate, as these parameters also are important for limiting membrane fouling. Furthermore, optimisation of process temperature and of pH has also been identified as important parameters for improving the microfiltration performance.
However, even though much development has been going on over the years regarding membranes, hardware and operational parameters, fouling is still today considered the one largest culprit to overcome for developing a successful microfiltration. This is in particular the case for microfiltration of products originating from fermentation broths.
The purpose of this invention is therefore to minimize fouling within microfiltration of fermented products.
It has surprisingly been found that activated carbon and elevated temperature may increase process capacity when microfiltrating a fermentation-derived product.
Therefore, the present invention provides:
A microfiltration process of a fermentation-derived product comprising adding activated carbon to a solution of the fermentation-derived product prior to or during the microfiltration process at a microfiltration process temperature of from 25xc2x0 C. to 65xc2x0 C.
The present invention deals with a new and surprisingly effective way of reducing fouling in microfiltration processes of fermentation-derived products.
It has surprisingly been found that fouling can be efficiently minimized in microfiltration processes when activated carbon is added prior to or during the microfiltration step.
It has also been found that a synergy exists between addition of activated carbon and the use of high temperature processing. The performance enhancement by carbon is found to be well suited for the modern microfiltration systems with back wash/back shock and systems with mechanical induced shear.
The use of activated carbon in relation to microfiltration is known from wastewater treatment and also from production of casein hydrolyzate where activated carbon in both cases is used for removing soluble impurities with the aim of improving product quality (WO 93/08702).
However, use of activated carbon with the purpose of minimizing fouling in microfiltration processes has not previously been applied within the biotechnology field.
An added advantage of introducing activated carbon for enhancement of microfiltration performance is that the added carbon in many cases bind unwanted impurities influencing the subsequent concentration or that otherwise needs to be removed by an added purification step for achieving acceptable product quality.
According to the present invention any fermentation-derived product of interest may be microfiltrated as described herein. Especially the method of the invention can be applied to purification of a protein.
In a preferred embodiment, the method is applied to enzymes, in particular to hydrolases (class EC 3 according to Enzyme Nomenclature; Recommendations of the Nomenclature Committee of the International Union of Biochemistry).
In a particular preferred embodiment the following hydrolases are preferred: Proteases: Suitable proteases include those of bacterial or fungal origin. Chemically modified or protein engineered mutants are included. The protease may be a serine protease or a metallo protease, preferably an alkaline microbial protease or a trypsin-like protease. Examples of alkaline proteases are subtilisins, especially those derived from Bacillus, e.g., subtilisin Novo, subtilisin Carlsberg, subtilisin 309, subtilisin 147 and subtilisin 168 (described in WO 89/06279). Examples of trypsin-like proteases are trypsin (e.g. of porcine or bovine origin) and the Fusarium protease described in WO 89/06270 and WO 94/25583.
Examples of useful proteases are the variants described in WO 92/19729, WO 98/20115, WO 98/20116, and WO 98/34946, especially the variants with substitutions in one or more of the following positions: 27, 36, 57, 76, 87, 97, 101, 104, 120, 123, 167, 170, 194, 206, 218, 222, 224, 235 and 274.
Preferred commercially available protease enzymes include Alcalase(trademark), Savinase(trademark), Primase(trademark), Duralase(trademark), Esperase(trademark), and Kannase(trademark) (Novozymes A/S), Maxatase(trademark), Maxacal(trademark), Maxapem(trademark), Properase(trademark), Purafect(trademark), Purafect OxP(trademark), FN2(trademark), and FN3(trademark) (Genencor International Inc.).
Lipases: Suitable lipases include those of bacterial or fungal origin. Chemically modified or protein engineered mutants are included. Examples of useful lipases include lipases from Humicola (synonym Thermomyces), e.g. from H. lanuginosa (T. lanuginosus) as described in EP 258 068 and EP 305 216 or from H. insolens as described in WO 96/13580, a Pseudomonas lipase, e.g. from P. alcaligenes or P. pseudoalcaligenes (EP 218 272), P. cepacia (EP 331 376), P. stutzeri (GB 1,372,034), P. fluorescens, Pseudomonas sp. strain SD 705 (WO 95/06720 and WO 96/27002), P. wisconsinensis (WO 96/12012), a Bacillus lipase, e.g. from B. subtilis (Dartois et al. (1993), Biochemica et Biophysica Acta, 1131, 253-360), B. stearothermophilus (JP 64/744992) or B. pumilus (WO 91/16422).
Other examples are lipase variants such as those described in WO 92/05249, WO 94/01541, EP 407 225, EP 260 105, WO 95/35381, WO 96/00292, WO 95/30744, WO 94/25578, WO 95/14783, WO 95/22615, WO 97/04079 and WO 97/07202.
Preferred commercially available lipase enzymes include Lipolase(trademark) and Lipolase Ultra(trademark) (Novozymes A/S). Amylases: Suitable amylases (xcex1 and/or xcex2) include those of bacterial or fungal origin. Chemically modified or protein engineered mutants are included. Amylases include, for example, xcex1-amylases obtained from Bacillus, e.g. a special strain of B. licheniformis, described in more detail in GB 1,296,839.
Examples of useful amylases are the variants described in WO 94/02597, WO 94/18314, WO 96/23873, and WO 97/43424, especially the variants with substitutions in one or more of the following positions: 15, 23, 105, 106, 124, 128, 133, 154, 156, 181, 188, 190, 197, 202, 208, 209, 243, 264, 304, 305, 391, 408, and 444.
Commercially available amylases are Duramyl(trademark), Termamyl(trademark), Fungamyl(trademark) and BANT(trademark) (Novozymes A/S), Rapidase(trademark) and Purastar(trademark) (from Genencor International Inc.).
Cellulases: Suitable cellulases include those of bacterial or fungal origin. Chemically modified or protein engineered mutants are included. Suitable cellulases include cellulases from the genera Bacillus, Pseudomonas, Humicola, Fusarium, Thielavia, Acremonium, e.g. the fungal cellulases produced from Humicola insolens, Myceliophthora thermophila and Fusarium oxysporum disclosed in U.S. Pat. Nos. 4,435,307, U.S. 5,648,263, U.S. 5,691,178, U.S. 5,776,757 and WO 89/09259.
Especially suitable cellulases are the alkaline or neutral cellulases having colour care benefits. Examples of such cellulases are cellulases described in EP 0 495 257, EP 0 531 372, WO 96/11262, WO 96/29397, WO 98/08940. Other examples are cellulase variants such as those described in WO 94/07998, EP 0 531 315, U.S. Pat. Nos. 5,457,046, U.S. 5,686,593, U.S. 5,763,254, WO 95/24471, WO 98/12307 and PCT/DK98/00299.
Commercially available cellulases include Celluzyme(trademark), and Carezyme(trademark) (Novozymes A/S), Clazinase(trademark), and Puradax HA(trademark) (Genencor International Inc.), and KAC-500 (B)(trademark) (Kao Corporation).
Oxidoreductases: Oxidoreductases that may be treated according to the invention include peroxidases, and oxidases such as laccases.
Peroxidases: An enzyme exhibiting peroxidase activity may be any peroxidase enzyme comprised by the enzyme classification (EC 1.11.1.7), or any fragment derived therefrom, exhibiting peroxidase activity.
Preferably, the peroxidase employed in the method of the invention is producible by microorganisms such as fungi or bacteria. Some preferred fungi include strains belonging to the subdivision Deuteromycotina, class Hyphomycetes, e.g., Fusarium, Humicola, Tricoderma, Myrothecium, Verticillum, Arthromyces, Caldariomyces, Ulocladium, Embellisia, Cladosporium or Dreschlera, in particular Fusarium oxysporum (DSM 2672), Humicola insolens, Trichoderma resii, Myrothecium verrucana (IFO 6113), Verticillum alboatrum, Verticillum dahlie, Arthromyces ramosus (FERM P-7754), Caldariomyces fumago, Ulocladium chartarum, Embellisia alli or Dreschlera halodes. 
Other preferred fungi include strains belonging to the subdivision Basidiomycotina, class Basidiomycetes, e.g. Coprinus, Phanerochaete, Coriolus or Trametes, in particular Coprinus cinereus f. microsporus (IFO 8371), Coprinus macrorhizus, Phanerochaete chrysosporium (e.g. NA-12) or Trametes (previously called Polyporus), e.g. T. versicolor (e.g. PR4 28-A).
Further preferred fungi include strains belonging to the subdivision Zygomycotina, class Mycoraceae, e.g. Rhizopus or Mucor, in particular Mucor hiemalis. 
Some preferred bacteria include strains of the order Actinomycetales, e.g., Streptomyces spheroides (ATTC 23965), Streptomyces thermoviolaceus (IFO 12382) or Streptoverticillum verticillium ssp. verticillium. 
Other preferred bacteria include Bacillus pumilus (ATCC 12905), Bacillus stearothermophilus, Rhodobacter sphaeroides, Rhodomonas palustri, Streptococcus lactis, Pseudomonas purrocinia (ATCC 15958) or Pseudomonas fluorescens (NRRL B-11).
Further preferred bacteria include strains belonging to Myxococcus, e.g., M. virescens. 
Particularly, a recombinantly produced peroxidase is preferred, e.g., a peroxidase derived from a Coprinus sp., in particular C. macrorhizus or C. cinereus according to WO 92/16634, or a variant thereof, e.g., a variant as described in WO 93/24618 and WO 95/10602.
Laccases and Laccase Related Enzymes: In the context of this invention, laccases and laccase related enzymes contemplate any laccase enzyme comprised by the enzyme classification (EC 1.10.3.2), any chatechol oxidase enzyme comprised by the enzyme classification (EC 1.10.3.1), any bilirubin oxidase enzyme comprised by the enzyme classification (EC 1.3.3.5) or any monophenol monooxygenase enzyme comprised by the enzyme classification (EC 1.14.18.1).
The microbial laccase enzyme may be derived from bacteria or fungi (including filamentous fungi and yeasts) and suitable examples include a laccase derivable from a strain of Aspergillus, Neurospora, e.g., N. crassa, Podospora, Botrytis, Collybia, Fomes, Lentinus, Pleurotus, Trametes, e.g., T. villosa and T. versicolor, Rhizoctonia, e.g., R. solani, Coprinus, e.g. C. plicatilis and C. cinereus, Psatyrella, Myceliophthora, e.g. M. thermophila, Schytalidium, Polyporus, e.g., P. pinsitus, Phlebia, e.g., P. radita (WO 92/01046), or Coriolus, e.g., C. hirsutus (JP 2-238885), in particular laccases obtainable from Trametes, Myceliophthora, Schytalidium or Polyporus.
Other preferred hydrolases are carbohydrolases, transferases, lyases, isomerases, and ligases.
The method of the invention may be applied to an untreated fermentation broth or to a fermentation broth that has first been subjected to, e.g., a pH adjustment, a temperature adjustment, a water dilution and/or one or more solid/liquid separatory techniques such as flocculation or centrifugation.
According to the present invention a microfiltration process means a membrane filtration separating soluble products from solids such as biomass and other particulate matter. Any membrane equipment known in the art may be used, but it is preferred that the membrane filtration is done using membrane techniques such as hollow fiber, tubular, or plate and frame units. The membranes may be made of a variety of materials such as polysulfone membranes (PS) or teflon (PTFE). The preferred cut off value will depend on the properties of the fermentation-derived product in question but usually a cut off value in the interval of from 200 kD to a pore size of 2 xcexcm is preferred.
According to the present invention activated carbon means any activated carbon known in the art; useful activated carbon types may be Acticarbon 4S #2228, available from Elf Atochem North America; Darco carbon KB-B, available from American Norit Co.; Calgon granular carbon, available from Pittsburgh Activated Carbon; or Picatif FGV 120, available from Pica, France.
According to the present invention the added amount of carbon is preferably from 0.05 to 2% (w/w) of the initial fermentation broth volume, in particular the added amount of carbon is from 0.1 to 1% (w/w) of the initial fermentation broth volume.
According to the present invention the microfiltration process is preferably carried out at a temperature of from 25xc2x0 C. to 65xc2x0 C.; preferably at a temperature of from 30xc2x0 C. to 60xc2x0 C.; more preferably at a temperature of from 30xc2x0 C. to 55xc2x0 C.; especially at a temperature of from 35xc2x0 C. to 50xc2x0 C.
If a pH adjustment is necessary any acid or base may be used, but formic acid or acetic acid are preferred as acids, and sodium hydroxide is preferred as base. The optimal pH is normally a compromise between the pH at which the fermentation-derived product of interest is most stable and the pH at which the solubility of the fermentation-derived product of interest is greatest.
The microfiltration process may be further improved if in addition to the carbon treatment an Al-product is added (see Example 3). The Al-product may be added to the fermentation broth prior to or during the microfiltration process.
According to the invention any soluble Al compound or any mixture thereof may be used, in particular Al2 (SO4)3, NaAlO2, Na2Al2O4, K2Al2O4, Al(NO3)3, AlCl3, Al-acetate, Al-formate, or polymer aluminiumhydroxychloride (e.g., EKOFLOCK available from Boliden).
According to the present invention the added amount of the Al-product is preferably from 1.4xc3x9710xe2x88x923 to 2.8xc3x9710xe2x88x921 (mol Al/w) of the initial fermentation broth volume, in particular the added amount of the Al-product is from 1.4xc3x9710xe2x88x922 to 1.4xc3x9710xe2x88x921 (mol Al/w) of the initial fermentation broth volume.
The microfiltration process may be further improved if in addition to the carbon treatment a Ca-product is added (see Example 4). The Ca-product may be added to the fermentation broth prior to or during the microfiltration process.
According to the invention any soluble Ca compound or any mixture thereof may be used, in particular CaSO4, Ca(OH)2, or CaCl2.
According to the present invention the added amount of the Ca-product is preferably from 1.6xc3x9710xe2x88x922 to 4.9xc3x9710xe2x88x921 (mol Ca/w) of the initial fermentation broth volume, in particular the added amount of the Ca-product is from 3.2xc3x9710xe2x88x922 to 3.2xc3x9710xe2x88x921 (mol Ca/w) of the initial fermentation broth volume.
The microfiltration process may be even further improved if in addition to the carbon treatment an Al-product and a Ca-product are added.
It should also be noted that the microfiltration process according to the present invention may be a batch process or a continuous process.
The fermentation-derived product achieved according to the invention may be further purified in a variety of ways such as by using ultrafiltration, evaporation, chromatographic methods, adsorption and/or crystallization processes.
The invention is further illustrated in the following examples which are not intended to be in any way limiting to the scope of the invention as claimed.